2.7 Symbiosis

Types of symbiosis on reefs

Symbiotic continuum - Parasitism -> Commensalism -> Mutualism

Commensal

• shrimpfish + sea urchins - the fish acquire protection rom urchin without affecting it

Mustualistic

• clownfish + anemones - fish gain protection from the stinging tentacles, clownfish act as bait to lure other fish in

• Remoras + sharks, large fish, and sea turtles - the remora uses a sucking disc to attach to the host, feeding on scraps and cleaning host of external parasites. Remora gets a free ride & protection, host rids itself of parasites

• cleaning shrimp or fish species + larger fish - cleaners get food, larger fish get cleaned

• Giant Clam + Symbiont - enlarged mantle houses symbionts, which are 'farmed' then transported to the digestive glands where they are digested (only once they are old or not functioning well)

• Coral + cyanobacteria: N-fixing bacteria live in the skeletons of hermatypic corals benefit from C production of the corals

• Sponge, jellyfish, coral + symbiont -

Parasitic

• viruses, bacteria, flatworms, roundworms, leeches + fish

• pearlfish + sea cucumbers - pearlfish live in the intestinal tract of sea cucumber and eat waste or sometimes healthy tissue

Symbiodiniacea

• unicellular algae that photosynthesize

• Pigmentation

  • Chlorophyl a

  • Chlorophyl c2

• Mutualistic relationship where both benefit

  • corals provide stable protected environment and an abundance of nutrients (CO2, N and P waste from cell resp in coral)

  • symbionts provide photosynthetic products (O2, energy rich organic macromolecules)

  • Symbionts produce 10-100 times more C than they need and almost all this excess is transported to the coral

• Obligate symbiosis - organisms like octocorals have lost the ability to heterotrophically feed, meaning they rely entirely on symbiosis

• Facultative symbiosis - corals can survive with or without symbiosis, and can expel or gather symbionts according to energetic needs

• Nutrient recycling within the oligotrophic waters

Species/ taxonomy

• Phylum: Myzozoa

  • SuperclassL Dinoflagellata

    • Class: Dinophyceae

      • Order: Suessiales

        • Family: Symbiodiniaceae

• clades A - I

References

Ferrier-Pages et al. 2018

Review of isotope methods on marine symbiosis. Talks about the use of N, C, and CSIA with a particular focus on corals. Lots of good diagrams showing energy, nutrient, macromolecule flow.

Baker 2001

Symbiont communities change after bleaching which may help with long-term survival.

Ferrier-pages 2022

Tested DIC and DIN assimilation to symbionts in two mesophotic genera, and quantified translocation to the host. They found that mesophotic corals can't rely on autotrophy to meet their metabolic needs and are N limited. This likely causes slowed growth rates. Morphology of the colony likely improves heterotrophic capcaity, represented by changes in assimilation & C:N ratios. These genera are likely limited to a narrow depth range because of their adaptations to survive there, and should be viewed as marginal reefs rather than refugia.

Wall 2020

The authors conducted SIA, ITS2 symbiont identification, and physiological methods on corals collected along a depth gradient. Light/depth influenced some of the factors, but many more were influenced by the symbiont community present. Durusdinium is believed to be more stress & bleaching tolerant compared to Breviolum or Cladocopium. Durusdinium or more stress-tolerant symbionts do not share as much with the coral. Isotope values did not follow expected patterns, with N values not reflecting trophic differences between symbiont and host (likely due to recycling between them). C values were affected by depth and symbiont type, reflecting acclimation or adaptation to energetic needs.

Reynaud 2009

First study to look at δ15N in symbionts and host under experimental feeding and light conditions. As expected, δ15N was lower in symbionts and trophic fractionation increased it in the host, but only by 1‰. Surprisingly, they found that fed corals had lower δ15N than starved ones, contradicting the expectation that 15N should accumulate in most consumer tissues as 14N is excreted. They also discussed the N-recycling, N-conservation, and N-limitation hypotheses.